6© 2012 Semtech Corporation
www.semtech.com
PRELIMINARY
PROTECTION PRODUCTS
RClamp1644T
Applications Information
Figure 1 - Pin Configuration (Top View)
Device Connection and Layout Options for Protecting
One USB Port
The RClamp1644T is optimized for protection of USB
ports. Low capacitance protection is provided for the
USB data (DM, DP) and USB ID pins. The maximum
capacitance on these lines is <0.60pF. USB Data and
ID lines are connected at pins 2, 3, and 4. These
inputs are referenced to an internal 5 volt TVS
protection device. When the voltage on these lines
exceed 5 volts, the TVS will conduct. Pin 1 is
connected to the USB voltage bus (VBus). This device
will conduct when the voltage on the bus exceeds 12
volts. Ground is provided at pin 5. Multiple micro vias
connected to ground are recommended for best ESD
performance. This will reduce parasitic inductance in
the ground path and minimize the clamping voltage
seen by the protected device. The package is
designed for easy trace routing. The VBus pin is
connected to the voltage layer of the PCB with a micro
via as shown. Connection to ground is made at pin 5
using two micro vias. Connection to the ID pin is
shown, however if the application does not utilize the
ID function, pin 4 can be left not connected.
The flow through layout combined with extremely low
capacitance means the RClamp1644T will have
minimal effect on high speed signal integrity. A typical
USB 2.0 eye diagram test result with RClamp1644T is
shown in Figure 3.
Figure 2 - PCB Layout Example
1
VBus
GND
DM
DP
ID
2
Figure 3 - USB Eye Pattern with RClamp1644T
Assembly Guidelines
The small size of this device means that some care
must be taken during the mounting process to insure
reliable solder joint. The table below provides
Semtech's recommended assembly guidelines for
mounting this device. The figure at the right details
Semtech’s recommended aperture based on the
below recommendations. Note that these are only
recommendations and should serve only as a starting
point for design since there are many factors that
affect the assembly process. The exact manufactur-
ing parameters will require some experimentation to
get the desired solder application.
